An image forming apparatus such as a laser printer or a copying machine is provided with a process cartridge that is attachable to and detachable from a body of the image forming apparatus (hereinafter, may be referred to as an “apparatus body”).
The process cartridge is a member that forms contents to be displayed, such as text or figures, in an attitude of being mounted to the apparatus body and transfers the contents onto a recording medium such as paper. Therefore, the process cartridge includes a photosensitive drum on which the contents to be transferred are formed and charging means and developing means for forming the contents to be transferred on the photosensitive drum.
Regarding the process cartridge, for maintenance, the same type of process cartridge is attached to or detached from the apparatus body, or an old process cartridge is separated from the apparatus body to be replaced with a new process cartridge and then the new process cartridge is mounted to the apparatus body. Attachment and detachment of the process cartridge can be performed by a user of the image forming apparatus themself, and from this point of view, it is preferable that attachment and detachment be performed as easy as possible.
The photosensitive drum included in the process cartridge needs to be rotated during operation. The photosensitive drum is provided with an end portion member (bearing member) to which a driving shaft of the apparatus body is engaged directly or via another member such that the photosensitive drum is rotated by receiving a rotational force from the driving shaft.
On the other hand, in order to attach and detach the process cartridge to and from the apparatus body, the engagement between the driving shaft of the apparatus body and the bearing member provided in the photosensitive drum needs to be released (separated) or re-engagement therebetween is needed on each occasion.
In Patent Documents 1 and 2, there are techniques disclosed in which the driving shaft that moves in the axial direction is provided on the apparatus body side and a twisted hole having a polygonal cross-section is formed in the driving shaft while a polygonal columnar protrusion that is inserted into the twisted hole of the driving shaft and transmits the driving force is included on the photosensitive drum side as the bearing member. The protrusion described in Patent Document 1 has a twisted column shape corresponding to the twisted hole of the driving shaft. On the other hand, the protrusion described in Patent Document 2 has a columnar shape that is not twisted.
In any of the techniques described in Patent Documents 1 and 2, an object thereof is to enhance the rotational precision of the photosensitive drum and reliably transmit the driving force to the photosensitive drum from the apparatus body.